<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>背景特效</title>
</head>
<body>
  <canvas id="magic" width="1267" height="918" style="position: fixed; top: 0px; left: 0px; z-index: -2; opacity: 0.5;"></canvas>
  <!-- <script src="./canvas-magic.js"></script> -->
  <script type="text/javascript">
  ! function() {
      //封装方法，压缩之后减少文件大小
      function get_attribute(node, attr, default_value) {
          return node.getAttribute(attr) || default_value;
      }
      //封装方法，压缩之后减少文件大小
      function get_by_tagname(name) {
          return document.getElementsByTagName(name);
      }
      //获取配置参数
      function get_config_option() {
          var scripts = get_by_tagname("script"),
              script_len = scripts.length,
              script = scripts[script_len - 1]; //当前加载的script
          return {
              l: script_len, //长度，用于生成id用
              z: get_attribute(script, "zIndex", -1), //z-index
              o: get_attribute(script, "opacity", 0.5), //opacity
              c: get_attribute(script, "color", "0,72,255"), //color
              n: get_attribute(script, "count", 99) //count
          };
      }
      //设置canvas的高宽
      function set_canvas_size() {
          canvas_width = the_canvas.width = window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth,
          canvas_height = the_canvas.height = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
      }

      //绘制过程
      function draw_canvas() {
          context.clearRect(0, 0, canvas_width, canvas_height);
          //随机的线条和当前位置联合数组
          var all_array = [current_point].concat(random_lines);
          var e, i, d, x_dist, y_dist, dist; //临时节点
          //遍历处理每一个点
          random_lines.forEach(function(r) {
              r.x += r.xa,
              r.y += r.ya, //移动
              r.xa *= r.x > canvas_width || r.x < 0 ? -1 : 1,
              r.ya *= r.y > canvas_height || r.y < 0 ? -1 : 1, //碰到边界，反向反弹
              context.fillRect(r.x - 0.5, r.y - 0.5, 1, 1); //绘制一个宽高为1的点
              for (i = 0; i < all_array.length; i++) {
                  e = all_array[i];
                  //不是当前点
                  if (r !== e && null !== e.x && null !== e.y) {
                          x_dist = r.x - e.x, //x轴距离 l
                          y_dist = r.y - e.y, //y轴距离 n
                          dist = x_dist * x_dist + y_dist * y_dist; //总距离, m
                      dist < e.max && (e === current_point && dist >= e.max / 2 && (r.x -= 0.03 * x_dist, r.y -= 0.03 * y_dist), //靠近的时候加速
                          d = (e.max - dist) / e.max,
                          context.beginPath(),
                          context.lineWidth = d / 2,
                          context.strokeStyle = "rgba(" + config.c + "," + (d + 0.2) + ")",
                          context.moveTo(r.x, r.y),
                          context.lineTo(e.x, e.y),
                          context.stroke());
                  }
              }
              all_array.splice(all_array.indexOf(r), 1);

          }), frame_func(draw_canvas);
      }
      //创建画布，并添加到body中
      var the_canvas = document.createElement("canvas"), //画布
          config = get_config_option(), //配置
          canvas_id = "c_n" + config.l, //canvas id
          context = the_canvas.getContext("2d"), canvas_width, canvas_height,
          frame_func = window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame || function(func) {
              window.setTimeout(func, 1000 / 45);
          }, random = Math.random,
          current_point = {
              x: null, //当前鼠标x
              y: null, //当前鼠标y
              max: 20000
          };
      the_canvas.id = canvas_id;
      the_canvas.style.cssText = "position:fixed;top:0;left:0;z-index:" + config.z + ";opacity:" + config.o;
      get_by_tagname("body")[0].appendChild(the_canvas);
      //初始化画布大小

      set_canvas_size(), window.onresize = set_canvas_size;
      //当时鼠标位置存储，离开的时候，释放当前位置信息
      window.onmousemove = function(e) {
          e = e || window.event, current_point.x = e.clientX, current_point.y = e.clientY;
      }, window.onmouseout = function() {
          current_point.x = null, current_point.y = null;
      };
      //随机生成config.n条线位置信息
      for (var random_lines = [], i = 0; config.n > i; i++) {
          var x = random() * canvas_width, //随机位置
              y = random() * canvas_height,
              xa = 2 * random() - 1, //随机运动方向
              ya = 2 * random() - 1;
          random_lines.push({
              x: x,
              y: y,
              xa: xa,
              ya: ya,
              max: 6000 //沾附距离
          });
      }
      //0.1秒后绘制
      setTimeout(function() {
          draw_canvas();
      }, 100);
  }();

  </script>
</body>
</html>
